The present device relates to an engine starter, particularly to the improvement of a braking current restriction means for an electric motor for starting an engine.
There is known an engine starter disclosed in the Japanese Utility Model Application No. 8696/89. The engine starter is described with reference to FIG. 1. The engine starter 1 is a magnet-employing starter of the electromagnetic push-in type and includes a DC motor 2 and an electromagnetic switch 3 attached to the motor. The DC motor 2 includes a permanent magnet having magnetic poles 4 for driving an armature 5 of the motor, and plus and minus brushes 6 and 7 disposed in slip contact with the armature. The electromagnetic switch 3 includes a main contact unit 8 consisting of a pair of fixed contacts 9a and 9b and a movable contact 11, which is put into and out of touch with the fixed contacts by a movable iron core 10, a pair of normally-closed fixed contacts 12a and 12b opposed to the movable contact 11, a current coil 13 for attaching the movable iron core 10, and a voltage coil 14 for keeping the iron core attracted. The 16. The normally-closed fixed contact 12a is grounded. The current coil 13 and the plus brush 6 are grounded when the electromagnetic switch 3 is de-energized. The other normally-closed fixed contact 12b is connected to the current outgoing terminal 17 of the current coil 13 and to the normally open fixed contact 9b .
Since the field means of the DC motor 2 of the conventional engine starter 1 described above entirely made of the permanent magnet 4, a high voltage is generated between the plus and the minus brushes 6 and 7 when the armature 5 is inertially rotated in the magnetic field of the permanent magnet. Besides, since the brushes 6 and 7 are grounded at that time, a braking current of excessive magnitude flows so that the contacts are fuse-bonded, the components of the electromagnetic switch 3 are thermally deteriorated and the armature 5 is abruptly stopped making a loud noise. These are problems.
It is an object of the present invention to provide an engine starter in which a braking current generated due to the inertial rotation of an armature is restricted.
In accordance with the above object the invention provides an engine starter comprising an electric motor for starting an associated engine when the motor is energized, and an electromagnetic switch including a pair of normally opened contacts connected to each other to form an energizing circuit for the motor at the time of energizing a coil of the switch, and a pair of normally closed contacts connected to each other to form a grounding circuit through a restrictive output device for said motor at the time of de-energizing the coil. A first restriction means restricts the kinetic energy generated due to the inertial rotation of the armature, and a second restriction means restricts a braking electrical current due to the rotation of the armature in a magnetic field. The first restriction means includes a permanent magnet and at least one pair of electromagnets neighboring each other. The second restriction means includes the restrictive output device.